1. Field of the Invention
The present invention relates to a high speed linear motor with a precise positioning ability, more particularly, a high speed linear motor having a precise positioning ability characterized in that the motor""s primary side is stationary and the motor""s secondary is moving at high speed.
2. Descriptions of the Prior Art
Machinery operating at high speed and efficiency is widely used in miscellaneous industrial applications such as a wafer carrier, a high-speed wafer probe, etc. There are two major categories of high-speed linear motion machinery, namely, a ball screw driven by a rotary motor and a linear motor. A ball screw converts a rotary motor""s rotation into linear motion, while a linear motor is a direct drive mechanism.
In a conventional machine, a ball screw is fixed in position by bearings and coupled to a rotary motor. As the ball screw rotates with the motor, its nut is driven to make linear movements. However, the problems of insufficient stiffness of the ball screw shaft and backlash existing between contacting parts result in the positioning error of a work piece. Furthermore, slippery motion between contact surface of the ball screw and the bearings brings about a frictional resistance that retards the moving speed (about 60 m/min) and the acceleration (usually below 1 G), and generates heat loss as well. In addition, an uneven frictional abrasion between the moving and the stationary parts of the ball screw assembly further affects machine""s positioning ability. Consequently, the durability of the machine is greatly reduced, and so is its lifetime. Besides, a conventional machine operating as such has been notorious for its awkwardness in appearance and bulkiness in size, which results in taking up more space for installation in a plant.
In a linear motor direct drive machine, the linear motor has a stationary part formed of a serrated structure with a ferromagnetic substance, and a moving part formed of an electromagnet and possibly a permanent magnet as well. The moving part moves relative to the stationary part. In a linear motor, its primary side may be an electromagnet whose magnetic field is built up by a current flowing through its winding thereof, while the secondary side is a serrated structure formed of the ferromagnetic substance. In such a structure, it is surely no problem when the linear motor operates at low speed, but in case it operates at high speed, the connection joints in the moving part are easily broken when the moving part reciprocates rapidly thereby shortening the motor""s lifetime. In order to prevent such a fault, the aforementioned joint portions shall be checked from time to time or even replaced in a predetermined period, thereby, incurring great inconvenience to users.
In view of the foregoing situation, the inventor of this invention herein conducted intensive research based on many years"" experience gained through professional engagement in the manufacturing of related products, with continuous experimentation and improvement culminating in the development of the precisely constructed high-speed linear motor of the invention herein.
It is the objective of the present invention to provide high speed linear motor (HSLM) with a precise positioning ability which is characterized in operating reliably and powerfully with high speed and acceleration, excellent positioning accuracy, minimum frictional loss, yet constructed in a compact size.
To achieve the aforementioned objective, the HSLM of the present invention comprises a stationary part and a moving part, wherein the moving part is formed of a ferromagnetic substance without any wire connection therein; while the stationary part is constructed of several field magnet modules whose windings are mutually connected so as to build up a magnetic field for operating the HSLM. It is a noteworthy feature of this structure that no worry of conductor disconnection when the moving part moves at high speed since there is no wire connected to it. For provision of a definite track for the moving part to attain a powerful driving force, the HSLM of the present invention is formed into a sandwiched structure. The stationary part is composed of an upper primary structure and a lower primary structure disposed at two sides of the moving part respectively. Both primary structures are constructed of several field magnet modules which are separated by a non-wearing bearing, such as an air bearing to support the moving part between the upper and the lower primary structures of the stationary part. With the field magnet modules at both sides of the moving part, the intensity of the magnetic field will be at least doubled compared to that of a conventional linear motor with the field magnet modules at one side only. The aforementioned objective is thus easily achieved by the HSLM of the present invention.
Finally, a position sensor for the HSLM, if installed, is equipped on the stationary part instead of on the moving part so as to prevent the interruption of signals from disconnection of the signal wires when the motor operates at high speed.